1. Field of the Invention
The present invention relates to an electromagnetic clutch, and more particularly to an electromagnetic clutch suitable for a compressor of a vehicle air-conditioning system.
2. Description of the Related Art
An electromagnetic clutch of this type is suitable for a compressor of a vehicle air-conditioning system and capable of intermittently transmitting a driving force from the engine to the main shaft of the compressor. For instance, the well-known electromagnetic clutch disclosed in Unexamined Japanese Patent Publication No. 11-63021 is provided with a rotor that is rotatably supported by the end of the housing of the compressor. The rotor has an electromagnetic coil inside, and a driving belt is put round the outer periphery of the rotor with an engine pulley. Disposed coaxially with the rotor is an annular armature plate. The armature plate is contactable to and separatable from the end wall of the rotor and is also rotatable integrally with the main shaft of the compressor. More specifically, the armature plate is coupled to the main shaft through a coupling member and plate springs, and is elastically supported by the plate springs.
According to this electromagnetic clutch, when the electromagnetic coil is not excited, the armature plate is located at the OFF position that is away from the rotor due to the urging force of the plate springs. When the electromagnetic coil is excited, however, the armature plate is displaced from the OFF position to the ON position in which it is joined to the rotor. In other words, the armature plate is displaced toward the rotor, resisting the urging force of the plate springs due to the attraction of the electromagnetic coil, and is pressed against the rotor. At this point, the rotor is driven to rotate through the driving belt, so that the rotor brings the armature plate to rotate therewith through the use of a frictional force, to thereby rotate the main shaft of the compressor through the plate springs and the coupling portion.
The above-described electromagnetic clutch requires that the armature plate be disposed parallel to the rotor with high accuracy in order to achieve the secure couplement of the armature plate with the rotor. For this reason, both the coupling member and the plate springs supporting the armature plate require high accuracy not only in their shapes and dimensions but also in assembly.
In case that the supporting means of the armature plate is constructed with the coupling member and the plate springs, there occurs a problem that the number of components of the supporting means are increased, and that it is difficult to improve the accuracy in assembly.